Radio Preppers

General Category => Technical Corner => Topic started by: solaris0121 on May 18, 2018, 02:46:15 AM

Title: Modding MTR4b for 13.8 volts..... possible ?
Post by: solaris0121 on May 18, 2018, 02:46:15 AM
So Ive decided I really want an mtr4b...... but Im struggling with the fact that it wont take over 12 volts like most others do.  Being able to plug into a car battery would be a key factor for the prepper side of my brain

Can it be modded easily ?  I was thinking I could add a second power socket for 13.8 volts but not sure exactly what parts are needed to drop the voltage.  Id like to add a couple of banana plug/screw terminals for easy field use.  Id keep the original power socket for smaller batteries and maybe add a switch to flip between them ?

Love to hear your thoughts.  Regards, sean.
Title: Re: Modding MTR4b for 13.8 volts..... possible ?
Post by: gil on May 18, 2018, 05:24:30 AM
Hello,

You could use a 7812 voltage regulator, make a car adapter with it.. Otherwise, three Lithium Ion cells will give you 12.6V max, which works. You put that little 7812 in a little plastic box in your car and you're good to go. You could even put it inside the MTR4b with a switch and add a DC input jack for higher voltages...

Gil.
Title: Re: Modding MTR4b for 13.8 volts..... possible ?
Post by: solaris0121 on May 18, 2018, 08:48:47 AM
Thanks Gil,  id want something wired internally to run directly off car batteries/battery terminals  - im keen to have it all self contained if possible - I might even remove it all from the original box and re-box it with a ZM-2 (or similar)  in a single (more solid) case.... and a little active loudpspeaker and a switchable keyer.....along the lines of those project boxes youve been using lately.   Then I get options for resonant antennas, random wires and much more.

THe lithium Ion batteries - are they the 18650 you have been using.....   that was the plan for portable generally and the screw terminals for "emergency" power when required.

With an adjustable 7812 regulator I suppose I can adjust the transmit power as well.
Title: Re: Modding MTR4b for 13.8 volts..... possible ?
Post by: RadioRay on May 18, 2018, 09:56:16 PM
If you simple need a voltage drop (not a current drop!) a couple of garden variety diodes usually give you a 0.9 volt drop per diode.  So, your 13.7ish can RUNNING can have diodes in the power line to drop it below 12 VDC , using your /cigar' lighter/power plug in the car.  I have a bunch of 1N400X series power supply diodes I've de-soldered from junk power supplies, which used for this at no cost.


>RadioRay  ..._  ._
Title: Re: Modding MTR4b for 13.8 volts..... possible ?
Post by: gil on May 19, 2018, 04:11:26 AM
The 7812 is not adjustable.. I did the diode thing once but the drop was more like 0.4V 1N4004..
Gil

Sent from my SM-G928F using Tapatalk

Title: Re: Modding MTR4b for 13.8 volts..... possible ?
Post by: Jon_Garfio on May 22, 2018, 05:12:02 AM
You need a voltage regulator or a step down.

Example:

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F162867196965

Enviado desde mi Redmi Note 4 mediante Tapatalk

Title: Re: Modding MTR4b for 13.8 volts..... possible ?
Post by: CroPrepper on May 22, 2018, 06:11:26 AM
You need a voltage regulator or a step down.

Example:

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F162867196965

Enviado desde mi Redmi Note 4 mediante Tapatalk

And some ferrit cores wound before it enters the radio I guess. Somewhere I read about extreme noise created from those regulators.
Title: Re: Modding MTR4b for 13.8 volts..... possible ?
Post by: Jon_Garfio on May 13, 2019, 09:54:22 AM
I remember 78xx needs almost 2v above the output voltaje to works fine,  If you want 12v and use a 7812, the component needs almost 14vcc.